1. Technical Field
The invention relates to a load driving apparatus. Particularly, the invention relates to a load driving apparatus related to a light-emitting diode (LED) lamp and a method thereof.
2. Related Art
In the past two decades, engineers dedicated to develop new illumination light sources. The European Union specifically makes a “rainbow project”, and provides four conditions requiring the new illumination light source to satisfy, which are respectively high efficiency, energy saving, pollution-free, natural light simulation.
Since a light-emitting diode (LED) has the above advantages, and is incomparable relative to a conventional illumination light source (for example, an incandescent lamp and a fluorescent lamp), the LED is regarded as the most valuable “green” light source in the 21st century, and replaces the incandescent lamp and the fluorescent lamp to become a leading product in the market.
Regarding an LED lighting device having a pulse width modulation (PWM)-based structure and a dimming function, a driving device therein that is used for providing an operation voltage to an LED lamp generally turns off the LED lamp by directly pulling down the operation voltage of the LED lamp, so as to achieve the purpose of lamp-off.
However, the conventional technical manner/solution for lamp-off probably causes malfunction or failure of a PWM controller in the driving device (due to that a working voltage supplied to the PWM controller is lower than an under voltage lockout (UVLO) voltage of the PWM controller), which results in a fact that the LED lamp cannot be again turned on after it is turned off unless the PWM controller in the driving device is restarted (for example, high voltage (HV) start).
In order to resolve the problem that the LED lamp cannot be again turned on after it is turned off, a feasible solution is to increase winding turns of a transformer corresponding to the working voltage of the PWM controller in the driving device, though a voltage regulator circuit has to be additionally configured to provide the working voltage required by the PWM controller. In this way, not only additional power loss is produced to reduce conversion efficiency, additional cost thereof is also high.
On the other hand, under a design condition that the PWM controller does not have a latch over current protection (OCP) function, once the LED lamp is shorted, the PWM controller periodically/intermittently outputs a PWM signal with a very short duty cycle (since it is easy to reach an OCP point built in the PWM controller) to switch a power switch transistor in the driving device, which causes unnecessary and repetitive high power loss.